Throughout this disclosure, various publications, patents and published patent specifications are referenced by an identifying citation. Also within this disclosure are Arabic numerals referring to referenced citations, the full bibliographic details of which are provided immediately preceding the claims. The disclosures of these publications, patents and published patent specifications are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
Congestive heart failure has been recognized as an emerging epidemic in developed countries. In the United States, it is estimated that 4.9 million people suffer from heart failure with an annual incidence of 550,000. Since cardiomyocytes possess very limited regenerating capability, survivors of myocardial infarction, the most common cause of heart failure, often progress to heart failure due to massive myocardial loss. Heart transplantation is currently the last resort for end-stage heart failure, but this is hampered by a severe shortage of donor organs and immune rejection. Thus, cell-based therapies have emerged as promising alternatives.
Human embryonic stem cells (hESCs) possessing the ability to self-renewal and to differentiate essentially into all cell types of our bodies (pluripotency) including highly specialized cells such as cardiomyocytes, hold the promise to replenish/repair cellular functions through cellular transplantation. Prior studies have demonstrated that cellular transplantation of hESC-derived cardiomyocytes to damaged myocardium can improve ventricular contractile function and thus improving congestive heart failure (1-4).
Indeed, hESC-derived CMs (hESC-CMs) display structural and functional properties of early-stage cardiomyocytes (CM), and can functionally integrate with or even electrically pace the recipient heart after transplantation in vivo. Thus, hESCs have the potential to act as an unlimited ex vivo source of cells for transplantation and cell-based therapies of otherwise incurable heart diseases.
However, any cell or tissue utilized for heart tissue reconstitution or transplantation must produce electrically excitable heart tissue with viable calcium handling and contractile functions to mechanically pump blood throughout the body. It has been reported that spontaneously beating hESC-CMs do not have the capacity to mimic a mature cardiomyocyte because they lack functional sarcoplasmic reticulum (SR). The SR is a specialized organelle of cells typically found in smooth and striated muscle. It is a type of smooth endoplasmic reticulum and is defined by its function to store and pump calcium (Ca2+) ions. The sarcoplasmic reticulum contains large stores of calcium, which it sequesters and then releases when the cell is depolarized thus triggering muscle contraction.
During an action potential of adult CMs, Ca2+ entry into the cytosol through sarcolemmal L-type Ca2+ channels triggers the release of Ca2+ from the intracellular Ca2+ stores (a.k.a. SR) via the ryanodine receptor (RyR). This process, the so-called Ca2+-induced Ca2+ release (CICR), escalates the cytosolic Ca2+ ([Ca2+]i) to activate the contractile apparatus for contraction. In mature ventricular CMs, efficiency of CICR is further improved due to the presence of transverse (t)-tubules or invaginations in the sarcolemma that brings the L-type Ca2+ channels closer to RyRs, therefore, decreasing the diffusion distance for Ca2+ enabling faster and synchronized activation of CICR across the cell. For relaxation, elevated [Ca2+]i is pumped back into the SR by the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) and extruded out of the cell by the Na+—Ca2+ exchanger (NCX) to return to the resting [Ca2+]i level. Such a rise and subsequent decay of [Ca2+]i is known as Ca2+ transient. Given the central importance of CICR in cardiac excitation-contraction (EC) coupling, proper Ca2+ handling properties of hESC-CMs are therefore crucial for their successful functional integration with the recipient heart after transplantation. Indeed, abnormal Ca2+ handling, as in the case of heart failure, can even be arrhythmogenic (e.g. delayed after depolarization). Furthermore, integration of immature hESC-CMs with weaker contractile force relative to the mature CMs in vivo can lead to heterogeneous strain in recipient heart, leading to progression of cardiac hypertrophy and/or arrhythmias.
Thus, it would be beneficial to understand the properties of hESC-CMs with the goal of designing effective strategies or protocols for improving safety and efficiency of hESC-CM transplantation. This invention satisfies this need and provides related advantages as well.